Pressure measurement in microwave-assisted chemical synthesis

ABSTRACT

A pressure-measuring vessel system for microwave assisted chemical processes is disclosed. The vessel system includes a pressure resistant vessel that is otherwise transparent to microwave radiation, a pressure-resistant closure for the mouth of the vessel, with portions of the closure including a pressure resistant synthetic membrane, a pressure transducer external to the vessel, and a tube extending from the transducer, through the membrane and into the vessel for permitting the pressure inside the vessel to be applied against the transducer while the closure and membrane otherwise maintain the pressure resistant characteristics of the vessel.

FIELD OF THE INVENTION

The present invention relates to microwave-assisted chemistry, and inparticular relates to a microwave instrument that offers particularadvantages useful for chemical synthesis reactions.

BACKGROUND OF THE INVENTION

The present invention relates to devices and methods formicrowave-assisted chemistry. As generally recognized in the chemicalarts, many chemical reactions can be initiated or accelerated byincreasing the temperature—i.e. heating—the reactants. Accordingly,carrying out chemical reactions at elevated (i.e., above ambient)temperatures is a normal part of many chemical processes.

For many types of chemical compositions, microwave energy provides anadvantageous method of heating the composition. As is well recognized inthe art, microwaves are generally categorized as having frequencieswithin the electromagnetic spectrum of between about 1 gigahertz and 1terahertz, and corresponding wavelengths of between about 1 millimeterand 1 meter. Microwaves tend to react well with polar molecules andcause them to rotate. This in turn tends to heat the material under theinfluence of the microwaves In many circumstances, microwave heating isquite advantageous because microwave radiation tends to interactimmediately with substances that are microwave-responsive, thus raisingthe temperature very quickly. Other heating methods, includingconduction or convection heating, are advantageous in certaincircumstances, but generally require longer lead times to heat any givenmaterial.

In a similar manner, the cessation of application of microwaves causesan immediate corresponding cessation of the molecular movement that theycause. Thus, using microwave radiation to heat chemicals andcompositions can offer significant advantages for initiating,controlling, and accelerating certain chemical and physical processes.

In recent years, much interest in the fields of chemical synthesis andanalysis has focused upon the use, synthesis or analysis of relativelysmall samples. For example, in those techniques that are generallyreferred to as “combinatorial” chemistry, large numbers of small samplesare handled (e.g., synthesized, reacted, analyzed, etc.) concurrentlyfor the purpose of gathering large amounts of information about relatedcompounds and compositions. Those compounds or compositions meetingcertain threshold criteria can then be studied in more detail using moreconventional techniques.

Handling small samples, however, tends to present difficulties inconventional microwave-assisted instruments. In particular, small massesof material are generally harder to successfully affect with microwavesthan are larger masses. As known to those of ordinary skill in this art,the interaction of microwaves with responsive materials is referred toas “coupling.” Thus, stated differently, coupling is more difficult withsmaller samples than with larger samples.

Furthermore, because of the nature of microwaves, specifically includingtheir particular wavelengths and frequencies, their interaction withparticular samples depends upon the cavity into which they aretransmitted, as well as the size and type of the sample being heated.

Accordingly, in order to moderate or eliminate coupling problems,conventional microwave techniques tend to incorporate a given cavitysize, a given frequency, and similarly sized samples. Such techniquesare useful in many circumstances and have achieved wide acceptance anduse. Nevertheless, in other circumstances when one of theseparameters—sample size, material, microwave frequency—is desirably ornecessarily changed, the cavity typically has to be re-tuned in order toprovide the appropriate coupling with the differing loads. Statedsomewhat differently, and by way of illustration rather than limitation,in a conventional device a one gram load would require tuning differentfrom a ten gram load, and both of which would require different tuningfrom a hundred gram load, and all of which would differ if the microwavefrequency or type of material is changed.

As another issue, differently-sized samples are generally mostconveniently handled in reaction vessels that are proportionally sizedbased on the size of the sample. Many instruments for microwave-assistedchemistry, however, are—for logical reasons in most cases—made to handlevessels of a single size; e.g. instruments such as described in U.S.Pat. No. 5,320,804 or open vessels as described in U.S. Pat. No.5,796,080. Thus although such instruments are valuable for certainpurposes, the are generally less convenient, and in some cases quiteineffective for samples, vessels, and reaction other than a certain size(volume) or type.

As yet another issue, many reactions proceed more favorably underincreased (i.e. above atmospheric) pressure. Controlling and usingincreased pressures for small samples in microwave-assisted chemistrycan, for the reasons stated above and others, be somewhat difficult.

Accordingly, the need exists for new and improved instruments formicrowave assisted chemistry that can handle small samples, canconveniently handle a variety of sample sizes and vessel sizes and thatcan incorporate and handle higher pressure reactions when desired ornecessary.

OBJECT AND SUMMARY OF THE INVENTION

Therefore, it is an object of the invention to provide a microwaveinstrument suitable for chemical synthesis and related reaction and thatcan handle small samples, can conveniently handle a variety of samplesizes and vessel sizes and that can incorporate and handle higherpressure reactions when desired or necessary.

The invention meets this object with an instrument formicrowave-assisted chemical processes that avoids tuning discrepanciesthat otherwise result based upon the materials being heated. Theinstrument comprises a source of microwave radiation a waveguide incommunication with the source, with at least a portion of the waveguideforming a cylindrical arc, a cylindrical cavity immediately surroundedby the cylindrical arc portions of the waveguide, and at least 3 slottedopenings in the circumference of the circular waveguide that providemicrowave communication between the waveguide and the cavity.

In another aspect the invention is a method of conducting organicsynthesis reactions comprising applying microwave radiation to a sampleusing a frequency to which the sample (solvent, etc) will thermallyrespond, and optimizing the coupling between the applied microwaves andthe (load) sample without adjusting the physical dimensions of thecavity, without physical movement of the cavity (i.e. no tuning screws),without physical movement of the position of the sample and withoutadjusting the frequency of the applied microwaves as the sample heatsand as the reaction proceeds.

In another aspect, the invention is a pressure-measuring vessel systemfor microwave assisted chemical processes. In this aspect, the inventioncomprises a pressure resistant vessel (i.e., it resists the expectedpressure to which it is expected to be exposed) that is otherwisetransparent to microwave radiation, a pressure-resistant closure for themouth of the vessel, with portions of the closure including a pressureresistant synthetic membrane, a pressure transducer external to thevessel, and a tube extending from the transducer, through the membraneand into the vessel for permitting the pressure inside the vessel to beapplied against the transducer while the closure and membrane otherwisemaintain the pressure resistant characteristics of the vessel.

In another aspect, the invention is an instrument for microwave-assistedchemical processes that provides greater flexibility in carrying outmicrowave-assisted chemistry under varying conditions. In this aspect,the instrument comprises a source of microwave radiation, a cavity incommunication with the source, with the cavity including at least onewall formed of two engaged portions that form a barrier to thetransmission of microwaves when so engaged, with the engaged portionsbeing disengagable from one another; and with one of the portionsfurther including a microwave-attenuating opening for receiving areaction vessel therethrough and into the cavity when the portions areengaged.

In yet another aspect, the invention is a method of increasing theefficiency of microwave-assisted chemical reactions. The methodcomprises carrying out a first chemical reaction in a reaction vessel inan attenuated cavity of a microwave instrument, removing the reactionvessel and the attenuator from the instrument, placing a differentreaction vessel and a differently-sized attenuator in the same cavity ofthe instrument, and carrying out a second chemical reaction in thedifferent vessel in the cavity of the instrument.

The foregoing and other objects and advantages of the invention and themanner in which the same are accomplished will become clearer based onthe followed detailed description taken in conjunction with theaccompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front perspective view of an instrument according to thepresent invention;

FIG. 2 is a rear perspective view of the instrument illustrated inFigure one;

FIG. 3 is a partially exploded interior view of the instrumentillustrated in FIGS. 1 and 2;

FIG. 4 is a perspective view of a cavity and wave-guide according to thepresent invention;

FIG. 5 is an interior view of the waveguide and cavity illustrated inFIG. 4.

FIG. 6 is a perspective exterior view of the wage guide, cavity andmagnetron of the present invention;

FIG. 7 is a perspective view of the pressure-measuring assemblyaccording to the present invention;

FIG. 8 is another perspective view of the pressure-measuring assembly;

FIG. 9 is a detailed exploded view of the pressure measuring assembly;

FIG. 10 is an exploded view of the cavity assembly of an instrumentaccording to the present invention;

FIG. 11 is a cross-sectional view of a reaction vessel,pressure-measuring means and collet assembly of an instrument accordingto the present invention;

FIG. 12 is a cross sectional view of the cavity portion of theinstrument according to the invention and including an exemplaryreaction vessel; and

FIG. 13 is a cross-sectional view almost identical to FIG. 12, butillustrating the features of the invention in relation to adifferently-sized reaction vessel.

FIG. 14 is a cross sectional view of a reaction vessel.

FIG. 15 is a cross sectional view of a reaction vessel in accordancewith the present invention.

DETAILED DESCRIPTION

An embodiment of the present invention is illustrated in perspectiveview in FIG. 1 with the instrument broadly designated at 20. Most of theother details of the invention will be shown in other drawings, but FIG.1 illustrates that the instrument 20 includes a housing 21, a controlpanel 22, and a display 23. As will be discussed later herein, thecontrol panel 22 can be used to provide the instrument with a variety ofinformation that may relate to the chemical processes being carried out,or to set or define certain parameters, such as maximum pressure ortemperature during the application of microwave energy to a particularreaction. The control panel 22 can be formed of any type of appropriateinput devices, with buttons 24 being illustrated. It will be understood,however, that other types of input devices, including touch screens,keyboards, a computer “mouse” or other input connections from computersor personal digital assistants can also be used in any appropriatefashion known to those of skill in this art that does not otherwiseinterfere with the operation of the instrument. Similarly, the display23 is most commonly formed of a controlled or addressable set of liquidcrystal displays (LCDs) but can also comprise a cathode ray tube (CRT),light emitting diodes (LEDs), or any other appropriate display medium.

The housing 21 includes a removable upper portion 25, attached byappropriate fasteners 26 (screws or Allen nuts are exemplary) to a lowerhousing portion 27 and a pedestal portion 30, which in turn aresupported by the pedestal feet 31.

FIG. 1 also illustrates that the housing 21 includes an opening 32,which provides access to the microwave cavity in a manner that will bedescribed with respect to other drawings. As FIG. 1 illustrates, theopening 32 provides much easier access for placing samples into thecavity than in many other types of microwave instruments.

FIG. 1 also illustrates the sample holder and microwave attenuatorassembly 33, and a collet assembly 91 which will likewise be describedin more detail with respect to other of the drawings.

FIG. 2 is a rear perspective view of an instrument according to thepresent invention that illustrates some additional items. As in FIG. 1,FIG. 2 illustrates the upper housing portion 25, the lower housingportion 27, the fasteners 26, the pedestal portion 30, the feet 31, thesample holder and attenuator assembly 33 and the opening 32 in thehousing 25 that provides access to the cavity.

Additionally, FIG. 2 illustrates that the device includes at least onecooling fan 34 with a second being shown at 35. The fans 34 and 35 serveto cool the electronics and the magnetron portions of the device, aswell as helping to keep the cavity from becoming overheated in thepresence of ongoing chemical reactions. Other than having the capacityto appropriately cool the instrument and the cavity, the nature orselection of the fans can be left to the individual discretion of thosewith skill in this art.

FIG. 2 also shows the power switch 36 and the power cord inlet 37. Inorder to take advantage of the full capacity of the instrument, inpreferred embodiments, the instrument includes the parallel port 41 andthe serial port 40 for receiving input from or providing output to otherelectronic devices, particularly microprocessor based devices, such aspersonal computers, personal digital assistants or other appropriatedevices. Similarly, FIG. 2 illustrates a connector 42 for the pressuretransducer to be described later herein.

FIG. 3 is a partially exploded view of the interior of an instrument 20according to the present invention. In common with FIGS. 1 and 2, thelower portion 27 of the housing and the pedestal portion 30 of thehousing are both illustrated along with the pedestal feet 31. FIG. 3also illustrates several of the fasteners 26, as well as the fan 34along with its housing 42.

FIG. 3 shows the display 23 in exploded fashion along with a firstelectronics board 43 and a second electronics board 44. Basically, theelectronics carried by the boards 43 and 44 are generally wellunderstood in their nature and operation. With respect to the instrumentof the present device, the electronics first control the power from agiven source, usually a wall outlet carrying standard current. Theelectronics also control the operation of the device in terms of turningthe magnetron on or off, and in processing information received from theongoing chemical reaction, in particular temperature and pressure. Inturn, the appropriate processor is used to control the application ofmicrowaves, including starting them, stopping them, or moderating them,in response to the pressure and temperature information received fromthe sensors described later herein. The use of processors and relatedelectronic circuits to control instruments based on selected measuredparameters (e.g. temperature and pressure) is generally well understoodin this and related arts. Exemplary (but not limiting) discussionsinclude Dorf, The Electrical Engineering Handbook, Second Ed. (1997) CRCPress LLC.

In the embodiment illustrated in FIG. 3, the outer housing of the cavityis visible at 45, along with the housing portions of the microwavesource, illustrated as the magnetron 46. FIG. 3 also illustrates thesample holder and attenuator assembly 33, and a motor 47 for stirringreactants in a manner described later herein. FIG. 3 also illustratesthe housing 50 for the second fan 35 present in the illustratedembodiment. Because the sample vessel (not shown) and the sample holderand attenuator assembly 33 are generally quite different in size thanthe cavity itself, FIG. 3 illustrates that the attenuator 33 accordingto the present invention further includes an upper rim 51 into whichlower portions of the sample holder and attenuator assembly 33 can restin a changeable receiving fashion. The features, advantages and detailsof the attenuator 33 are discussed in more detail with respect to FIGS.11, 12, and 13. The attenuator 33 is in turn held in place by a pair ofretaining rings 52 and 53 into which the attenuator 33 is received andwhich is also held in place by the interlock assembly broadly designatedat 54.

FIGS. 4 and 5 illustrate aspects of the waveguide and cavity portions ofthe instrument according to the present invention. In theseillustrations, the waveguide is broadly designated at 55, and includesboth a parallelpiped rectangular portion 56, and a cylindrical portion57 that in preferred embodiments has a rectangular cross section. In theillustrated embodiment, the waveguide 55 is supported on a series oflegs 60 which serve to position the cavity 61 and waveguide 55 incommunication with the magnetron 46 and the other elements within theparticular housing 21. One of the legs, designated at 96, has a slightlydifferent structure to support the motor 47 (not shown). It will beunderstood, of course, that such features as the leg 60 which merelypositions the waveguide within a particular embodiment are not limitingof the present invention. In preferred embodiments the rectangular orparallelpiped portion 56 of the waveguide joins the cylindrical portion57 perpendicularly to a tangent defined by the circumference of thecylindrical waveguide portion 57.

FIGS. 4 and 5 also illustrate the cavity as broadly designated at 61. Inparticular, the cavity is formed by an inner cylindrical wall 62 thatforms a concentric cylinder inwardly of the cylindrical cavity housing45. An upper waveguide plate 63 and a lower waveguide plate 64 definethe limits of the waveguide 55 in both its rectangular portion 56 andits cylindrical portion 57. The waveguide 55 is constructed of amaterial that reflects microwaves inwardly and prevents them fromescaping in any undesired manner. Typically, such material is anappropriate metal which, other than its function for confiningmicrowaves, can be selected on the basis of its cost, strength,formability, corrosion resistance, or any other desired or appropriatecriteria. In preferred embodiments of the invention, the metal portionsof the waveguide and cavity are formed of stainless steel.

The top plate 63 (as well as the bottom plate 64) is also held in placeby a series of connectors 65 which can be rivets, screws or nuts,provided that their size and shape avoids undesired interference withthe microwaves in the cylindrical or other portions of the waveguide 55.

Perhaps most importantly, FIG. 4 illustrates that a plurality of slottedopenings 66 are present in the inner cavity wall 62 for facilitating thetransmission of microwaves from the waveguide 55 into the cavity 61. Itwill be understood that because the inner wall 62 defines the border ofthe waveguide 55 and the cavity 61, the slotted openings 66 can also bedescribed as being in the inner circumference of the cylindrical portion57 of the waveguide.

In particular, it has been discovered in accordance with the presentinvention that a plurality of such slots in a circular orientation in astatic structure in the cavity 61 provides an appropriate amount ofcoupling with a wide variety of sample sizes or types that may bepresent in the cavity. Although the inventors do not wish to be bound byany particular theory, it appears that the plurality of slots 66, permita variety of microwave patterns (modes) to be established in the cavity61, depending upon the load to which the microwaves are coupled. Thecavity includes at least three slots, preferably at least five, and inthe presently most preferred embodiment includes seven slots spaced atleast about 40 degrees from each other. Preferably, the slots 66 areoriented parallel to the axis of the cavity 61.

As other details, FIG. 4 illustrates a connector plate 67 and connectingpins 70 are at one end of the waveguide 55 for connecting the waveguide55 to the magnetron 46 or other microwave source, which can, dependingupon choice and circumstances, also comprise klystron, a solid statedevice, or any other appropriate device that produces the desired ornecessary frequencies of electromagnetic radiation within the microwaverange. FIG. 4 also shows a gas inlet fitting 58 that is part of a systemfor cooling the cavity that is discussed in more detail with respect toFIGS. 10, 12 and 13.

As some additional details, in the preferred embodiments, thecylindrical waveguide completes an arc of more than 180°, and preferablybetween 270° and 360°, and the cylindrical cavity 61 completes a full360°.

FIG. 5 shows the same details as FIG. 4, but in a broken line interiorview. Accordingly, FIG. 5 likewise illustrates the overall structure ofthe waveguide 55, its rectangular and cylindrical portions 56 and 57respectively, the cavity 61, the slots 66 in the inner wall 62, and thesupporting legs 60. FIG. 5 also illustrates that the fasteners 65 have arelatively low profile within the waveguide 55 to avoid interfering withmicrowave propagation therethrough.

In particular detail, FIG. 5 shows that the waveguide 55 is connected tothe magnetron 46 (not shown) through the launching opening 71 in theplate 67. The microwaves can then propagate through the rectangularportion of the waveguide 56 into the circular portion 57 of thewaveguide 55. The structure also includes two walls 72 and 73 that arepositioned in the cylindrical portion 57 of the waveguide just adjacentone of the places where it intersects with the rectangular portion 56.Accordingly, to the extent that standing waves or modes are in thewaveguide 55 and cavity 61, they will be confined to the illustratedgeometry by the reflecting wall 73. In the absence of the walls 72 or73, the modes in the waveguide and the cavity 61 would be quitedifferent because they would interact through a full 360° of thewaveguide housing rather than in the somewhat lesser portion than theydo in the illustrated embodiment.

FIG. 5 also shows that in the preferred embodiment of the presentinvention there are seven slots 66 in the inner cavity wall 62, witheach of the slots being at least about 40 degrees apart from each of thenext adjacent slots. Furthermore, none of the slots 66 are directly atthe end of the rectangular portion 56 of the waveguide 55 so that themodes that set themselves up in the waveguide 55 and cavity 61 mustenter the cavity 61 after having entered at least a portion of thecylindrical portion 57 of the waveguide 55.

FIG. 5 also illustrates that in preferred embodiments, the cavity floor74 includes a plurality of small openings 75 for ventilation and fluiddrainage purposes, with ventilation being expected and liquid drainagebeing less frequent, typically in the case of spills. FIG. 5 alsoillustrates a circular shaft 76 that depends from the floor 74 of thecavity 61 for permitting optical access to the cavity in a manner thatwill be described later herein.

Alternatively, FIG. 5 also illustrates the optional use of a cavityliner 59 for containing spills, splashes or other incidents in thecavity 61. The cavity liner 59 optionally includes a small opening 68 tofacilitate optical temperature measurement through the opening 76 in thecavity floor 74 and the window 69. If the cavity liner 59 is formed of amaterial that is transparent to the optical measurement (typicallyIR-transparent for IR temperature measurements), the window 69 may beunnecessary. The liner 59 is preferably formed of a chemically-resistantpolymer, and can (depending on the user's cost and benefits) provide adisposable alternative to physically cleaning reagents or by-productsfrom the cavity 61.

FIG. 5 also illustrates the dielectric insert 95 that is described inmore detail with respect to FIG. 10.

FIG. 6 is a complementary view of a number of the elements of theinvention and illustrates the cavity 61 from the perspective of itshousing 45 in conjunction with the rectangular portion 56 of thewaveguide 55 and the magnetron 46. In particular, FIG. 6 offers a largerview of the retaining rings 52 and 53 along with the removableattenuator 33. The attenuator 33 includes an axial opening that will bedescribed in more detail with respect to FIGS. 12 and 13. As describedwith respect to FIG. 3, the retaining rings and the attenuator 33 areheld in place by the interlock assemblies 54. One of the particularadvantages of the invention is that with the use of the retaining rings52 and 53, along with the interlock assembly 54 to retain the attenuator33 in place, the interlock assembly 54 can be relatively easilyreleased, and the attenuator 33 replaced with one that contains adifferent sized opening that in turn supports a different size reactionvessel while still preventing microwaves from propagating past theattenuator 33.

Thus, the retaining rings 52 and 53, along with the engaged attenuator33 form the upper horizontal wall of the cavity and a barrier to thetransmission of microwaves when so engaged. The retaining rings 52 and53 are fixed to the cavity (i.e., removable only by disassembling theinstrument with tools), while the attenuator 33 is easily removable fromthe rings 52 and 53 with a simple turning and lifting movement. Theremovable attenuator 33 includes the microwave attenuating opening 118(FIGS. 12 and 13) for receiving a reaction vessel therethrough, and intothe cavity 61. It will thus be understood that in preferred embodiments,the instrument comprises two or more of the removable and engagableattenuators 33 that have differently-sized (from one another)microwave-attenuating openings for receiving differently-sized reactionvessels.

FIGS. 7, 8, and 9 illustrate detailed aspects of the pressure measuringmeans of the instrument including the transducer assembly 38. FIG. 7shows the assembly 38 in assembled fashion with a series of retainingscrews 82, a collet adjustment slot 83, and a collet tension screw 84all of which are perhaps best understood with respect to FIG. 9.

FIG. 8 shows the backshell of the assembly 38, apart from the collethousing 86 which includes the retaining screws 82 that are alsoillustrated in FIG. 7. A pressure transducer 116 is positioned inside atransducer holder 123 which in turn is surrounded by the adjustablecollet assembly 91, the details of which are best illustrated in FIG. 9.

FIG. 9 is an exploded view of the transducer assembly 38. As in FIGS. 7and 8, the collet backshell is illustrated at 85, and the collet housingat 86. The setscrews 82 illustrated in FIGS. 7 and 8 are alsoillustrated in FIG. 9.

FIG. 9 is perhaps best understood with respect to its relation to avessel (not shown in FIG. 9) that is in the cavity 61 undergoing amicrowave-assisted chemical reaction. Such a vessel, and its cap, areschematically illustrated in somewhat more detail in FIG. 11, but forthe purposes of FIG. 9, it will be understood that a vessel would bepositioned under and in engagement with a vessel receptor 106 that isillustrated in FIG. 9. In order to engage the entire transducer assembly38, and in turn the pressure measuring transducer, with a vessel, thetransducer assembly 38 forms an adjustable device that can move inlinear relationship to its own housing 86, and with respect to a vesselin the cavity. Accordingly, and in order to accomplish this, FIG. 9shows that the transducer assembly 38 includes a plurality (four arepreferred) of collet leaves 107. The leaves 107 are held in flexiblerelationship to the collet trunk 110 by the garter spring 111. Amongother features, the collet trunk 110 includes a plurality of pins 112.As a result, when the leaves 107 are attached to the collet trunk 110 bythe garter spring 111, the leaves 107 can flex inwardly and outwardlywith respect to the overall axis of the assembly 38. Each leaf 107further includes a gripping edge 113 that engages a cap on a vessel in amanner that is illustrated in FIG. 11. FIG. 9 also shows that theretaining screws 84 are received into the threaded bolts 114. In use,the threaded bolts 114 are received into the openings 119 in the collettrunk 110 and the screws 84 are received into the threaded bolts 114.The screws 84 can move parallel to the axis of the assembly 38 in thecollet adjustment slots 83 that are also illustrated in FIGS. 7 and 8.The two-part nature of the screws 84 and 114 permit the collet 86housing and the collet leaves 107 to be tightened in place in anappropriate relationship to a vessel as may be desired or necessary ingiven circumstances.

The present invention measures the pressure inside of a vessel bytransmitting the pressure through a needle that extends through a septumand into the vessel to the transducer 116 that converts the pressureinto an appropriate electrical signal for the processor or the display.FIG. 9 also illustrates these features in more detail as does FIG. 11.First, the needle 115 extends into the reaction vessel 105 (FIG. 11). Inturn, the needle 115 transmits the pressure, in the well-understoodfashion of fluid mechanics, to the transducer 116. In turn, thetransducer 116 transmits its signals through the wires 117. In a typicalarrangement (and although not specifically illustrated in FIG. 9), thetransducer 116 includes four wires: power and its ground, and signal andits ground.

The other elements in the left-hand portion of FIG. 9 help maintain thetransducer 116 and the needle 115 in proper relationship with each otherand with the vessel. Thus, FIG. 9 shows a needle holder 120, which isfixed on the collet adjustment housing 86 using the screws 121 which arerespectively received in the screw holes 122 in the housing 86. Thetransducer 116 is received in a transducer holder 123 that also enclosesa needle receptor 124 that receives the upper (cap) portion 125 of theneedle 115. The transducer 116 includes a small bushing 126 thatreceives the needle receptor 124, with the O-ring 127 providing anadditional pressure seal. The A clip ring 130 helps hold these elementstogether in the transducer holder 123. FIG. 9 thus illustrates that whenthe collet assembly and transducer assembly are properly assembled, theneedle 115 passes axially through the needle holder 120, the housing 86,the collet trunk 110, and the vessel receptor 106, and into the vesselitself, thus permitting the transducer to read the pressure in thevessel as desired.

FIG. 10 illustrates additional features of the instrument of the presentinvention in exploded fashion. A number of the elements illustrated inFIG. 10 have already been described with respect to the other figures.These include the magnetron 46, the rectangular portion 56 of thewaveguide 55, the circular portion 57, the retaining rings 52 and 53,and the interlock assembly 54. FIG. 10 illustrates the attenuator in aresting, but not fully engaged position with respect to the retainingring 52. A polymer bushing 51 is positioned between the retaining rings52 and 53 and helps provide a better physical and microwave seal for thecavity 45.

FIG. 10 also illustrates a dielectric insert 95 that fits in the cavity61 immediately adjacent the inner wall 62 of the cavity 61. Thedielectric insert 95 serves at least two purposes: first, the dielectricinsert 95 is preferably formed from a chemically inert material to helpprotect the interior of the cavity 61 from reagents. Preferred materialsinclude polymeric fluorinated hydrocarbons such aspolytetrafluoroethylene (PTFE).

Second, the insert 95 forms a portion of a preferred system for coolingthe interior of the cavity 61 during or after chemical reactions havebeen carried out therein and in response to the elevated temperaturesgenerated by the reactions. In particular, in preferred embodiments, thewaveguide 55 includes a gas inlet fitting (58 in FIGS. 4 and 6) throughwhich a cooling gas can be circulated into and throughout the waveguide.In order to take advantage of this, the insert 95 includes thecircumferential channel 98 through which the cooling gas can flow. Aseries of small, radially-oriented openings (too small to be illustratedin the scale of FIG. 10) permit the gas to flow into the center of thecavity 61 and cool it and any vessels and reagents inside. Although theinsert 95 changes the tuning characteristics of the cavity, the tuningcan be adjusted as desired to compensate for the insert 95. Such tuningis familiar to those of ordinary skill in this art and can be carriedout without undue experimentation.

FIG. 10 also illustrates the stirring mechanics of the instrument of thepresent invention. As illustrated therein, the stirrer motor 47 ispositioned on a motor platform leg 96 from which it drives a pulley 97.In turn, the drive pulley 97 drives a belt 100 to thereby drive thedriven pulley 101. The driven pulley 101 contains one or two magnets102, which, because of their position on the driven pulley 101, orbitthe center of the bottom floor 64 of the cavity 61. When a magneticstirrer bar is placed in a vessel in the cavity 61 and the motor 47drives the pulleys 97 and 101, the motion of the magnets 102 will inturn drive the stirrer bar in the reaction vessel.

FIG. 10 also illustrates a liquid drain 103. The liquid (fluid) drain103 works in conjunction with the floor openings 75 that are bestillustrated in FIG. 5 to allow any fluids that may collect in the cavity61 to drain through the openings 75 and then through the drain 103 to acollection point (not shown) which in a presently preferred embodimentcomprises a small removable trough located at the floor of theinstrument 20.

FIG. 10 further illustrates means for measuring the temperature of items(vessels and reagents) in the cavity, shown as the temperature measuringdevice 104, which is positioned immediately below and coaxially with thedepending shaft 76 (FIG. 5) to thus have an optically clear view of theinterior of the cavity 61. Accordingly, when the temperature measuringdevice is an optical device, with an infrared sensor being preferred, itcan accurately measure the temperature of vessels or contents of vesselswithin the cavity and provide the appropriate feedback to the processorof the instrument. As known to those familiar with such measurements,the infrared sensor 104 must be appropriately positioned and focused torecord the proper temperature of the intended objects, but doing so isgenerally well understood by those of skill in this art and will not beotherwise described in detail. Indeed, particular and appropriateadjustments can be made on an instrument-by-instrument basis withoutundue experimentation.

In preferred embodiments, the temperature measuring device 104 is aninfrared sensor, of which appropriate types and sources are well knownby those of skill in this art. Additionally, and although notillustrated in detail in FIG. 10, the driver pulley 101 also carries aninfra-red transparent window through which the sensor 104 can read theinfrared transmissions from the cavity 61. In preferred embodiments, thewindow is formed of an amorphous composition of germanium (Ge), arsenic(As) and selenium (Se), which provides the greatest accuracy, but at arelatively high cost. Thus, in other embodiments the window can beformed of infrared-transparent polymers such as polytetrafluoroethylene(PTFE) or polypropylene which provide accurate transmission at agenerally lower cost.

With respect to both pressure and temperature measurement, and theprocessors referred to earlier, the instrument includes the capabilityfor moderating the application of microwave power in response to themeasured temperature or pressure. The method of moderating can beselected from among several methods or apparatus. A simplewell-understood technique is to carry out a simple “on-off” cycle orseries of cycles (i.e., a duty cycle). Another technique can incorporatea variable or “switching” power supply such as disclosed in commonlyassigned U.S. Pat. No. 6,084,226; or techniques and devices thatphysically adjust the transmission of microwaves, such as disclosed incommonly assigned U.S. Pat. Nos. 5,796,080 and 5,840,583.

FIG. 11 is a cross-sectional view of the relationship between theremovable attenuator 33, a reaction vessel 105, and the collet assembly91. In a broad sense, FIG. 11 illustrates the relationship between thepressure transducer 116, the needle 115, and the closure for the vessel,which is formed of the deformable metal portion 133 and the septum 134.The relationship is such that the collet assembly 91 urges thetransducer 116 and needle 115 towards the vessel 105 while concurrentlybearing against the septum 134 and while urging the vessel and collettowards one another to provide the appropriate pressure seal.

By urging the various elements together in such fashion, the inventionprevents the puncturable septum from becoming a weak point in thepressure integrity of the vessel 105 and the transducer 116. As wellrecognized in this art, many chemical reactions will generate gases andin a closed system these generated gases will cause a correspondingincrease in gas pressure.

Many of the items illustrated in FIG. 11 are also illustrated in FIG. 9and, thus, corresponding numerals will be used in each case. In moredetail, the vessel 105 rests in the central opening 118 defined by theremovable attenuator 33. As illustrated in FIG. 11, the vessel 105includes an annular lip portion 109 that rests upon the inner opening118. In order to maintain the vessel in place while measuring thetemperature, the leaves 107 of the collet assembly are brought to bearagainst the removable attenuator 33 and, because of the threadedrelationships between the vessel receptor 106, the collet trunk 110, andthe collet housing 86, the collet can be brought to an appropriateposition and tightened there to maintain the leaves 107 in forcedcontact against the removable attenuator, while at the same time urgingthe vessel receptor 106 downwardly against the vessel 105. In turn, theposition of the collet trunk 110 with respect to the collet housing 86can be adjusted using the collet adjustment slot 83 and the threaded nutand bolt portions 84 and 114.

Accordingly, FIG. 11 shows that when the vessel is in place in theremovable attenuator 33, the collet assembly 91 can clamp it in placeand at the same time maintain an appropriate pressure against the septum134, while at the same time seating the needle 115 and its upper needleportion (cap) against the transducer in a manner which permits thepressure to be accurately measured, while at the same time maintainingthe integrity of the vessel and preventing it from becoming dislodgedwhen gases generated by the reaction increase the pressure in the vessel105.

FIG. 11 illustrates that the reaction vessel 105 includes a closureshown as the cap assembly 132. The cap assembly 132 is, in preferredembodiments, formed of a deformable metal ring 133 and a penetrableseptum 134. The septum 134 is made of a material, preferably anappropriate polymer or silicone related material, that can be penetratedby the needle 115, but which will surround and seal against the needle115 even after penetration, thus maintaining the pressure integrity ofthe vessel 105. The ring 132 is formed of a metal thick enough to haveappropriate pressure resistant properties, but which can be deformedrelatively easily, preferably with an ordinary clamping tool, to engagethe lip portions 135 of the reaction vessel 105 and thereby seal thevessel. With the vessel so sealed by the cap assembly 132, the leaves107 of the collet assembly 91, are brought into engagement with theattenuator 33 and the vessel 105, with the ledges or gripping edges 113engaging the attenuator 33 in a horizontal fashion and the cap assembly132 in a vertical fashion to help maintain the sealed integrity of theentire assembly when in use.

In this fashion, the needle 115 extends from the transducer, through thecap 132 and into the vessel 105 to provide pressure communicationbetween the interior of the vessel 105 and the transducer 116. Thecollet assembly 91 engages the transducer, the needle 115, the cap 132and the vessel 105 in linear relationship so that the pressure in thevessel 105 is transmitted to the transducer 116 while the vessel is inuse (i.e., a reaction taking place while microwaves are being applied).

FIGS. 12 and 13 illustrate some of the additional advantages of theremovable attenuator system of the present invention. Many of the itemsillustrated in FIGS. 12 and 13 have also been previously described withrespect to the other Figures, and in such cases the same referencenumerals will again refer to the same items. Both FIG. 12 and FIG. 13are cross-sectional views with FIG. 12 being taken directly through thecenter of the cavity 45 and FIG. 13 being taken from a point at which anentire vessel is illustrated.

FIG. 12 shows the cavity housing 45, the inner cavity wall 62, thedielectric insert 95, and the removable attenuator 33. As illustrated inFIGS. 12 and 13, in the preferred embodiments of the invention theremovable attenuator 33, which comprises the second portion of the twoengaged portions that together form the upper horizontal wall of thecavity (the other being retaining ring 52), the attenuator 33 comprisesan outer cylindrical wall 39 and an inner cylindrical wall 49, the innerand outer walls being separated by and perpendicular to an annular floor48. The inner wall 49 thus provides a receptacle for receiving thevessel 105 therein, and likewise provides the attenuating functionrequired to prevent microwaves generated by the source and propagatedinto the cavity from propagating outside the cavity when the vessel 105is in place.

FIG. 13 is almost identical to FIG. 12 with the exception that the firstattenuator 33 has been replaced a second attenuator 33′ and the vessel105 has been replaced with the round bottom flask 105′ illustrated inFIG. 13. It will be immediately seen that the removable attenuators 33and 33′ provide a quick and easy method of exchanging reaction vesselswithout otherwise changing the size, capability, function or operationof the overall instrument 20. Thus, for a larger vessel such as 105′illustrated in FIG. 13, the outer wall 39 of the attenuator 33′ isessentially the same as the outer wall 39 of the attenuator 33 in FIG.12. The inner cylindrical wall 49′, however, is somewhat taller (in theorientation of FIG. 13), defines a larger diameter opening and providesfor an attenuating function even though the flask 105′ is larger thanflask 105. By way of brief comparison, prior devices (e.g., U.S. Pat.No. 5,796,080) have attempted to customize the attenuator in a permanentsense for one particular sized vessel. Accordingly, an instrument thatwas capable of handling a somewhat smaller vessel such as 105illustrated in FIG. 12 could not handle the larger vessel 105′illustrated in FIG. 13. Furthermore, because the attenuator had to besized to accommodate the largest possible reaction vessels being used,the attenuator had to be permanently large, rather than just largeenough for the particular vessel being used.

As one further advantage of the removable attenuators 33 and 33′, inprior devices the diameter of the attenuator opening was kept largeenough to receive the largest portion of the vessel. With respect toFIG. 13, this required the opening to be large enough to receive thebulb portion of the round bottom flash 105′. In turn, a larger diameteropening requires a taller (longer) attenuator to prevent microwaves frompropagating beyond the attenuator.

In contrast, and as FIG. 13 illustrates, in the present invention, theattenuator need only be large enough to accommodate the nearby portionsof the vessel 105′ rather than the largest portions thereof. It willthus be understood as a further advantage that in some circumstances(e.g., FIG. 12) the attenuator 33 is put in place first, after which thevessel 105 is placed in the attenuator 33 and the cavity 61. In othercircumstances (e.g., FIG. 13), the vessel 105′ is placed in the cavity61 first, after which the attenuator 33′ is put into position.

Accordingly, in another aspect the invention comprises a method ofcarrying out chemical reactions using microwave assisted chemistry bycarrying out a first reaction in a first vessel of a particular size;removing the vessel and the attenuator 33 from the cavity; replacing thevessel with a new, differently sized vessel, and then replacing theattenuator with a new differently sized attenuator that neverthelessfits into the same opening.

FIGS. 14 and 15 illustrate some details of the reaction vessel 105. FIG.14 is a perspective view of the reaction vessel 105 alone, andillustrates that in certain (but not all) embodiments, it superficiallyrepresents a test tube in its cylindrical shape. As illustrated by thevessel 105′ in FIG. 13, the reaction vessel can be one of any number ofshapes and types while still incorporating the pressure-resistantaspects of the-invention. FIG. 14 also illustrates the deformable metalportion 133 of the cap, along with an opening for the septum 134 (notshown) through which the needle 115 (not shown) can penetrate in amanner described with respect to the other drawings.

As stated previously, the vessel 105 is preferably pressure resistant;i.e., it can withstand pressures above atmospheric. This capabilityenables reactions to be carried out at elevated pressures, which canoffer certain advantages in some circumstances. For example, particularreaction mechanisms can change in a favorable manner at above-ambientpressures, and in other circumstances, more efficient or even different(and better) mechanisms will take place at above ambient pressures.Additionally, under most circumstances, an increased pressure willproduce or maintain an increased temperature, in accordance with theideal gas law and its several related expressions. In turn, highertemperatures generally favorably initiate or accelerate most chemicalreactions.

FIG. 15 illustrates some additional details of the vessel 105. As showntherein, the vessel 105 has at least a cylindrical portion, and asillustrated in FIG. 15, may be entirely cylindrical, with thecylindrical portion being defined by the concentric inner and outerwalls 136 and 137 that terminate in a cylindrical opening 135. Asillustrated in FIG. 15, the cylinder includes an annular rim 140 thatextends outwardly from the circumference of the cylindrical opening 135and defines a rim circumference 141 that is concentric with thecylindrical portion of the vessel 105 and the cylindrical opening 135.

The vessel 105 further includes a curved outer wall portion 142 betweenthe concentric outer wall 137 and the rim circumference 141. In thisregard, it has been discovered that under higher pressures, aperpendicular relationship between the outer wall 137 and the rim 140tends to be the weakest point under stress applied from the interior ofthe vessel 105. It has been discovered according to the presentinvention, however, that by providing the curved outer wall portion 142,the pressure resistance of the vessel can be significantly increased.Specifically, in current embodiments, a reaction vessel with a 90-degreerelationship at the portion described will withstand pressures up toabout 200 pounds per square inch (psi) before failing. The curved outerwall portion 142 of the present invention, however, can withstandpressures of up to about 1000 psi.

The invention has been described in detail, with reference to certainpreferred embodiments, in order to enable the reader to practice theinvention without undue experimentation. A person having ordinary skillin the art will readily recognize that many of the components andparameters may be varied or modified to a certain extent withoutdeparting from the scope and spirit of the invention. Furthermore,titles, headings, or the like are provided to enhance the reader'scomprehension of this document and should not be read as limiting thescope of the present invention.

1. A pressure measurement assembly comprising: a pressure-resistantcylindrical vessel that is transparent to microwave radiation; a capassembly for closing said vessel; a pressure transducer external to saidvessel and said cap assembly; a needle for extending from saidtransducer, through said cap assembly and into said vessel, and forproviding pressure communication between the interior of said vessel andsaid transducer; and a collet for engaging and maintaining saidtransducer, said needle, said cap assembly and said vessel in linearrelationship by exerting a radial force inwardly against saidcylindrical vessel and an axial force linearly against said cap assemblyso that the pressure in said vessel is transmitted to said transducerwhile said vessel is in use.
 2. A pressure measurement assemblycomprising: a pressure-resistant cylindrical vessel that is transparentto microwave radiation; a cap assembly for closing said vessel, said capassembly comprising a mouth having a metal perimeter for gripping saidvessel and a penetrable septum surrounded by said metal perimeter; apressure transducer external to said vessel and said cap assembly; aneedle for extending from said transducer, through said cap assembly andinto said vessel, and for providing pressure communication between theinterior of said vessel and said transducer; and a collet for engagingand maintaining said transducer, said needle, said cap assembly and saidvessel in linear relationship by exerting a radial force inwardlyagainst said cylindrical vessel and an axial force linearly against saidcap assembly so that the pressure in said vessel is transmitted to saidtransducer while said vessel is in use; wherein said penetrable septummay receive said needle therethrough while maintaining a pressure sealto said vessel, said septum formed of a material selected from the groupconsisting of butyl rubber and siloxane polymers; wherein said vesselfurther comprises a means for securing said septum against pressure insaid vessel; and wherein said collet includes means for urging saidseptum towards said vessel while concurrently urging said vessel towardssaid transducer.